[AC-2503] Alloy: Migrations bugs

Hi Tony, I have two bugs regarding migration in Alloy. *Bug/unexpected result 1:* When doing a migration with the *sql* adapter, the script fails when executing migrations on first run on a fresh installed app. This is because the migration script will go through each migration, without creating the table beforehand. Hence, the first migration MUST include the definition of the table. e.g.

migration.up = function(migrator) {
	migrator.createTable({
		"columns": {
		    "id": "INTEGER",
		    "title": "TEXT",
		    "icon": "TEXT",
		    "type": "TEXT",
		    "parent_id": "INTEGER"
		}
	});
	
	migrator.db.execute('ALTER TABLE ' + migrator.table + ' ADD COLUMN sort INT;');
};

But this is not logical. In my opinion the best approach would be to have the adapter create the table if it does not exists and afterwards go through all the migrations. In this manner, the above migration should only be:

migration.up = function(migrator) {
	migrator.db.execute('ALTER TABLE ' + migrator.table + ' ADD COLUMN sort INT;');
};

Make sense? *Bug 2:* This might be a tooling issue, but here we go. When I want to create a new migration for a model, its not possible because it already have a migration. This is wrong, because the migrations are controlled by timestamps, so its the idea to have the same name. Please look at the attachment migration.png.